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EFFECT OF DISTORTION ON THE STRUCTURAL BEHAVIOUR OF THIN-WALLED STEEL REGULAR POLYGONAL TUBES RODRIGO GONÇALVES 1 , DINAR CAMOTIM 2 Abstract. This paper addresses the effect of cross-section distortion on the structural behaviour of thin-walled tubes with single-cell regular convex polygonal cross- sections (RCPS) and provides an in-depth view on the underlying mechanical aspects. In particular, the first-order, buckling (bifurcation) under uniform compression and undamped free vibration behaviours are characterised using the modal decomposition features and computational efficiency of a GBT (Generalised Beam Theory) specialization for RCPS recently developed by the authors [1]. Several analytical and illustrative numerical results are presented and discussed within the paper. Key words: thin-walled members, regular polygonal cross-sections, cross-section distortion, Generalised Beam Theory (GBT), buckling behaviour, vibration behaviour. 1. INTRODUCTION It is a well-known fact that cross-section distortion, which comprises both in- plane and out-of-plane (warping) displacements, can influence significantly the structural behaviour of open section thin-walled members. This phenomenon has been investigated rather intensively in the recent past and it may be argued that it is currently quite well understood, particularly for cold-formed steel lipped channel, zed, hat or “rack” section members. Much less known are the effects of distortion in thin-walled tubes with single-cell regular (equiangular and equilateral) convex polygonal cross-sections (RCPS), which are widely employed in slender structures such as lighting posts and telecommunication towers. The first papers on this subject were published only in the last year [1–3], where it was shown that, besides the well-known global and local (plate-type) deformation modes, the distortional modes also play a key role in the structural response of RCPS tubes, even in the case of geometrically linear problems. This paper addresses specifically the influence of cross-section distortion on the structural behaviour of RCPS tubes and aims at providing a general and broad 1 UNIC, Faculdade de Ciências e Tecnologia, Department of Civil Engineering, NOVA University Lisbon, 2829-516 Caparica, Portugal 2 ICIST, Instituto Superior Técnico, Department of Civil Engineering, Architecture and Georesources, University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
